Electronic devices are known which operate with a portable, removable user module or card having, for example, an integral microprocessor, a memory element, or both. Examples of such electronic devices include automated teller machines (ATM), pagers, personal digital assistants (PDA), and radiotelephones, such as cellular, wireless and cordless telephones. Examples of removable user modules include a subscriber identity module (SIM) which is used in portable telephones to communicate with a base station under specifications such as the Global System for Mobile Communication (GSM) specification.
With increased processing capability, improved audio and visual capability and expanded memory capability, users of portable devices have an increasing desire to download and view movies or music over wireless channels for playing on these portable devices. Because the content is typically stored and transmitted in a digital form, there is a substantial increased risk that the content may be illicitly intercepted, copied and redistributed for illegal gain. Unlike typical analog versions of video and music content, piracy of the digital form results in a very high quality reproduction of the content. Therefore, controlling unauthorized use of digital content is highly desirable.
Various cryptographic systems and techniques have been developed for securing content transmitted across a non-secure communications channel, however, these techniques are generally not suitable for controlling content when control of content's use is sought by several independent or distant entities. For example, a content provider may prefer that content be accessible by a user only when the user has sufficient credit to pay for the content use, while at the same time, the content provider desires to limit usage of the content to an authorized user.
Thus what is needed is a method and apparatus for reducing the risk of piracy when distributing and playing content. What is also needed is a method and apparatus that allows several entities to have control of content use and distribution.